Audio

Digital Recording Basics

Compressed Audio - MP3 (MPEG-1 audio Layer-3), WMA (Windows Media Audio) and AAC (Advanced Audio Coding) are three popular ways of compressing audio files. There are many more (see below). They both can compress files by a factor of 5 to 20 depending on the quality desired. MP3 is normally recorded at 128 Kbs for near CD quality and 64 Kbs for FM quality. Higher quality MP3 can be recorded at 192 - 320 Kbs. Although this is much lower than the 1.4 Mbs for CDs, it sound good because it compresses by discarding signals that are barely noticeable to the human ear.

WMA is a lossless format better for low bit rate encoding (16 - 64 Kbs), while MP3 is better for high bit rate (128 - 320 Kbs) encoding.

Variable Bit Rate (VBR) encoding encures consisteltly high audio quality by making intelligent bit-allocation decisions during encoding. VBR quality can be set from 1-100. VBR files may be larger than Constant Bit Rate (CBR) files at comparable encoding speed. e.g. at 128kbps a CBR file will usually be smaller than a VBR file at 50.

Some file types just contain the audio. But other file types can contain additional header information which can contain other information about the file (eg .dct files have information about the sender, priority, notes and other data in the file itself).
Source: File Formats at NCH Swift Sound

CD Qual (44.1 kHz 16-bit stereo WAV).:
AAC 128 kbs
MP3 160 kbps 9:1 coompression 1.5 MB/min
AAC 96 kbps
MP3 128 kbps 11:1 compression 1MB/min.
WMA 128 kbsp   750K/min
WAV    1:1 compression 10MB/min.
(AAC compressed audio at 96 kbps generally exceeded the quality of
MP3 compressed audio at 128 kbps. )

Near CD:
MP3 96 kbps 700k/min.
WMA 96 kbps 700K/min
Other:
AIFF @44.1 KHz using μLaw 2:1 16-bit	300M/hr.
AIIF @44.1 kHz using IMA 4:116-bit 	180M/hr.
AIIF @24 kHz using IMA 4:116-bit 	88M/hr.
AIIF @24 kHz using IMA 4:116-bit  mono	44M/hr.
AIIF @11 kHz using IMA 4:116-bit  mono	20M/hr.
AIFF @44.1 KHz using MACE 6:1 8-bit	57M/hr.

toll quality telephone (8 kHz 4-bit u-law) 64 kbs

cell phone quality (8 kHz GSM6.10) 13 kbs

 


Other Compression 

μLaw	2:1
MACE	3:1
MACE	6:1
ALaw	2:1
Qualcom PureVoice	

5.1

Dolby Digital sound with five primary speakers (front and rear/left and right plus center) and an LFE (suboofer) channel.

AA - Audible Audio

Audible file format (audio books) (Audible.com)

AAC - Advanced Audio Coding

An audio compression technology that is part of the MPEG-2 and MPEG-4 standards. AAC, especially MPEG-4 AAC, provides greater compression and superior sound quality than MP3.
ACC is at the core of the MPEG-4, 3GPP, and 3GPP2 specifications and is the new audio codec of choice for Internet, wireless, and digital broadcast arenas.

AC3

Adaptive Transform Coder 3 (relates to the bitstream format of Dolby Digital)

ADPCM - Adaptive Differential Pulse Code Modulation

takes up less storage space than the regular PCM format used by WAV and AIFF files.
Many MP3 players use ADPCM for their voice-recording feature.

AIFF/AIFC - Audio Interchange File

An old uncompressed digital audio file format from Apple. Similar to Microsofts WAV. AIFC is a compressed version.

ASF (Advanced Streaming Format)

ATRAC3 (Adaptive TRansform Acoustic Coding)

20:1 compression

AU Basic Audio

8-bit u-law. Old format from Sun.

Audible Audio Books

(AA)

CDA

The format of audio on a standard commercial Music CD (RedBook CD).

FLAC (Free Lossless Audio Codec)

An Lossless audio compression technology from the Xiph.Org Foundation (www.xiph.org). Files are much larger than MP3.

LFE

Low Frequency Effects. Frequencies from 10Hz to 120Hz, normally sent to a subwoofer. The 1 in 5.1

Lossless

A method of file compression in which audio data is not permanently discarded. While keeping all of a song's information results in a much bigger sound file, if preserving full audio fidelity is of highest importance, this is the way to go.

M4A

Apple iTunes AAC and Lossless format

Monkey's Audio

(.ape) - Lossless Compression format

MP3 MPEG-3

MPEG Audio Stream, Layer III

MP4 - MPEG-4

MPEG-4 is a Video format but has an audiio component

MPA - MPEG Audio Stream, Layer I, II or III

Ogg Vorbis (OGG)

open-source audio format created in response to the 1998 announcement by Fraunhofer to begin charging licensing fees for the use of its MP3 format.

RIAA

Recording Industry Association of America, an organization representing many music labels, from small indies to the majors. Find out more on its Web site.

Podcasting

An audio file, a MP3, most likely, in talk show format, along with a way to subscribe to the show and have it automatically delivered to your computerplayer. It uses RSS (see below). See PodcastingNews.com for software to let you subscribe to and manage podcasts on your PC.

RA/RAM

RealAudio

RAX

RealAudio 10. RealMedia Streaming file.

RSS - "Really Simple Syndication" or "Rich Site Summary"

A lightweight XML format designed for sharing headlines and other Web content. Used by Netscape to fill channels for Netcenter,

SD2 - Sound Designer II File

Can be played in QuickTime

SHN - Shorten files

It is a lossless compression algorithm for digital music developed by SoftSound.

VQF- Vector Quantization File

Transform-domain Weighted Interleave Vector Quantization (TwinVQF) Music File

WAV - Waveform Audio

PCM Wave audio. This is a raw audio file often used as the source for encoding other formats or burning CDs. There are several types of wav formats. The most common is PCM (44.1kHz,16 bit, stereo) at 600 MB per hour of audio. Others include low quality MP3 at 11.5kHz, 16kBit/s mono.

WMA - Windows Media Audio - lossless

Microsoft

See: Creating the right file (audio)
and Audio File Types
PC Audio Primer
File Formats at NCH Swift Sound

Radio:
Yahoo Radio
Windows Media
Audio Video over the Web under networks/internet

Digital Audio (MP3) Players:
See products.

Other Information:
Bill Machrone's SpA: Serious Personal Audio
MP3 Audio Page
Making WAV files from CDs
Understanding Digital Audio Formats Audio Formats and at wisc.edu Audio Input/Output Level Table Connecting your PC to a receiver

Video

NTSC Video (6 MHz)
Aspect Ratio: (3V x 4H)
Vertical Resolution:
A standard NTSC TV has 525 Horizontal Scan Lines (483 visable others contain sync signal)
    (PAL has 625 lines)
 Effective resolution is 483 x .7 (Kell factor) = 338 lines of resolution.
 (Kell Factor says that only 70% of detail is perceived
   because of information lost between scan lines.)

30 frames/second (2:1 interlaced - 1/2 of frames every 1/60 sec.)
Horizontal Resolution (vertical lines) varies:
  Older TV's are capable of 300 vertical lines
  Newer TV's have 400 lines and 27" and above "Hi Res." Std. TV's
  have 600-750 lines.
Broadcast
 (Analog): 230 
 Cable TV: 250 (330)
      VHS: 250
    S-VHS: 320 (400)
      Hi8: 350 (380-440)
   MiniDV: (400-520)
Digital 8: (400-500)
  MicroMV: (500)
Satellite: 450
      DVD: 480 (250-400)
       (most disks are recorded at 480 lines.
           DVD players may be capable of 540 lines resolution)
    (Horizontal resolution is measured based on a square screen, but actual
    resolution is 1.3 x because of the aspect ratio of 3:4)
    400 lines of resolution requires 400/.75 (aspec ratio)/ .7 (Kell factor) = 760 pixels)
    HDTV: 1080
    
DVD can use MPEG-1 or MPEG-2 compression, but most use MPEG-2.
Resolutions can be:
NTSC - 720x480, 704x480, 352x480 or 352x240
PAL - 720x576, 704x576, 352x576 or 352x288

See: Video Resolution at hometheater.about.com and here. 

Interfaces:
  Composite - Color and syncronization signals mixed (RCA phono connector)
  S-Video:  luminance (Y) and color information (C) transmitted on separate
            channels (4 pin Hosiden Connector )
            Resolution: 700x486 
  Component YUV - 3 channels  Y is the luminosity of the black and white signal.
     U and V are color difference signals (RCA plugs)
     Resolution: 480i, 480p, 576i, 576p, 720p, 1080i and 1080p depending on input.
  RGB - 3 channels Red/Green/Blue
  HDMI&tm; - High-Definition Multimedia Interface.
            HDMI is backward-compatible with most current DVI connections.
  DVI - Digital Visual Interface
A conventional NTSC image has 525 lines scanned at 29.97 Hz
with a horizontal resolution of 427 pixels.
This gives 3.35 MHz (assuming 2 pixels per video cycle) as a minimum
bandwidth to carry the video information without compression.

HDTV (US Version) (6MHz / 19.4Mbs)
  (HTDV signals are compressed to fit in the same 6MHz channel as std. TV)
   Broadcasters must convert to HDTV by 2006
Aspect Ratio: (9V x 16H)
HDTV is broadcast in two flavors: 1080i (interlaced) and 720p (progressive).

1080i has vertical resolution of 1125 (1080 active) lines,  so can show more detail.

But 720p has a faster frame rate (6o frames per sec0 vs 30 frames per sec),
so it is better for fast-moving action, and is free of field artifacts.

Newer HDTVs are 1080p with 60 fps, so can display both formats.

480 progressive (480p) (SDTV) Standard digital TV signal
Max. - 1080 interlaced (1080i) signal
Horizontal Resolution: Max. 1920
   Current HDTVs - 1200 - 1600 Lines
Uses MPEG-2 to compress signal to 19.4 Mbs
Transmitted over a 6 MHz UHF channel using a 8-VSB signal.
A standard (NTSC analog) signal is sent over the old VHF/UHF channel
while the HDTV (digital) signal is simulcast over a UHF channel (14-70)
In New York channels are allocated as follows:
Station Analog Digital
WCBS     2       56
WNYW     5       44
WNBC     4       28
WABC     7       45
WPIX    11       33
WNYE    27       24

QAM:
QAM decoding is under development due to the variations in Cable service providers. QAM256 generally has been reported to work, although QAM64 still poses problems with the decoding software. FusionHDTV QAM decoding is limited to only the non-encrypted channels available (generally the OTA local stations).

64 QAM carries 27 Mbps of information.
256 QAM carries 40 Mbps.
CableCARD tuners have to be Bi-directiona CableCARD tuners can use VOD (video on demand), impulse PPV (Pay per view), and cable customized electronic program guide.

See: Home Theater and Hi Fidelity

PC Video Resolution - here, tdc.co.uk, HDTV, Kell Factor, Resolution, Multimedia Information Representation

Formats:
See also: Video File Types

mpg, mpeg	
mov, qt	QuickTime
WMV	 Windows Movie 750K/min.
AVI	Microsoft Video Format
VDO	
ASF	Micorsoft Advanced Streaming Format
3GPP	3rd Generation Partnership Project for multimedia over 3rd gen. wireless.

VCD DAT, DivX, DV, IVF, DVD, VOB, XviD
DxVA

See: Digital Video - Camcorder and Digital Video - Software and Digital Audio (MP3) players under Products.
Audio Video over the Web under networks/internet

Terms

See Audio Formats Above and Audio File Types.
8-VSB	 8-level vestigial sideband - Modulation scheme for HDTV in the US
AC-3 - Active Coding-3 - 6 channel Dolby surround Anamorphic
Generally refers to the use of 16 x 9 aspect ratio pictures in a 4 x 3 system.
AAC - Advanced Audio Coding
ATSC Advanced Television Systems Committee ()
ATV - Advanced TV - Early name for DTV
CEMA - Consumer Electronics Manufacturers Association
DD Audio - Dolby Digital Audio
DTV - Digital TV (18 formats from SDTV to HDTV)
DVD - Digital Versatile Disk
DVI - Digital Visual Interface - Monitor interface with enough bandwidth for
       uncompressed HD signals. 
GA HDTV - Grand Alliance HDTV System (US standard)
HDMI™ - High-Definition Multimedia Interface.
         HDMI is backward-compatible with most current DVI connections.
HDTV - High Definition TV
NTSC - National TV Standards Committee
PPV - Pay per view
QAM (digital cable tuners) - Quadrature Amplitude Modulation
YC or Y/C - (luminance And Chrominance) A video system widely used for production video
YUV - Also  known as Y'CbCr and YPbPr) A production video system employing luminance
       and two chroma components (red and blue)
sound
SDTV - StanDard TV - The digital equivalent of the NTSC
RGB - Red,Green,Blue - Primary additive colors based on sensitivity of 3 pigments
in the cones in the retna of the human eye. (See: EE 498 at Wash. U.
VOD - video on demand

Glossaries at: HDTV Magazine, Crutchfield